Heretofore, there has been used a sealed battery having an electrode group housed in a case in a hermetically sealed manner. The electrode group includes positive and negative electrode plates, electrolyte, etc. Positive and negative external terminals connected to the positive and negative electrode plates respectively are arranged to protrude outside through the through holes and others of the case. Each terminal is fixed to the through hole of the case by for example riveting a rivet-like member. Usually, a seal member is placed between a base portion of the rivet member and the case to seal the inside of the case.
For instance, Patent Literature 1 proposes an electrode structure in which a gasket is sandwiched between a base portion of a rivet member and a case (a cover). Patent Literature 2 discloses a structure that a protrusion is formed in a seat surface so that the protrusion bites into a seal member, thereby improving sealing ability. Further, Patent Literature 3 discloses an electrode structure that an annular protrusion is formed in a seal member. In this literature, the protrusion is compressed to make sure sealing.